Operons contain multiple adjacent genes whose transcription is regulated by the transcription of a single polycistronic message. The processing of polycistronic pre-mRNA involves 3' end formation and trans-splicing by the specialized SL2 small nuclear ribonucleoprotein particle. In the June 20 Nature, Thomas Blumenthal and colleagues describe a screen for SL2-containing mRNAs in the Caenorhabditis elegans genome (Nature 2002, 417:851-854).

Blumenthal et al. used a probe enriched for SL2-containing mRNA to hybridize to microarrays containing over 17,000 genes. They selected around 1,200 genes, including many genes with known SL2-containing mRNAs. Most of these genes (86%) are located downstream in operons, indicating a strong correlation between SL2 trans-splicing and downstream location in an operon.

They estimated that the C. elegans genome might contain as many as 1,068 operons, representing over 2,600 genes (or up to 15% of genes).

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